1. Technical Field
The present invention generally relates to semiconductor fabrication and, in particular, to a system and method for aligning lithographic patterns using a bright spot created by a 0_xcfx80 phase conflict at the mask level and a frame (e.g., box or other structure) at the wafer level.
2. Background Description
Semiconductor devices are processed in levels. Materials are formed in layers and patterned, typically using lithographic processes. To build devices and components on semiconductor devices, layers of materials are employed. These layers must be properly aligned so that patterns and components on different layers line up and function correctly once fabricated. Lithographic alignment on prior levels is critical to ensure proper overlay. Lithographic alignment typically includes providing a bullet and target arrangement where the bullet is an alignment mark to be aligned against a target alignment mark.
These alignment marks may include features with sharp edges, for example, trenches or plateaus formed on a layer of the semiconductor device. In an alignment, a reticle of an optical alignment device is aligned to a mark on a stepper, and then the wafer of the semiconductor device is aligned to the mark on the stepper.
Conventional alignment techniques during lithography may suffer from poor signal-to-noise ratio due to variation in the film stack forming the alignment mark. A 0_xcfx80 phase conflict at the mask level generates a very bright spot when reflected light is measured.
The problems stated above, as well as other related problems of the prior art, are solved by the present invention, a system and method for aligning lithographic patterns using a bright spot created by a 0_xcfx80 phase conflict at the mask level and a frame (e.g., box structure) at the wafer level.
As noted above, a 0_xcfx80 phase conflict at the mask level generates a very bright spot when reflected light is measured. According to the present invention, alignment is obtained by superimposing this bright spot to a frame at the wafer level. As the frame may be, for example, a simple box structure, a simplified layout can be designed. Preferably, the frame is optimized to minimize the impact of film stack variations.
It is to be appreciated that because an alignment according to the present invention is performed directly between the mask and the wafer, the alignment is more accurate than that achieved by the prior art. The use of a bright spot transfers most of the burden of the illumination signal to the mask, alleviating the problems caused by film stack variation.
According to an aspect of the present invention, there is provided a method for aligning a semiconductor wafer and a mask. A semiconductor wafer is provided having an alignment mark formed thereon. A mask is provided having a pattern formed thereon. The mask is illuminated so as to create a bright spot thereon by a 0_xcfx80 phase conflict. The alignment mark is aligned with the bright spot, so as to align the semiconductor wafer with the mask.
According to another aspect of the present invention, the method further comprises the step of creating the alignment mark on the semiconductor wafer in a form of a frame.
According to yet another aspect of the present invention, the creating step comprises the step of creating the frame to minimize an impact of film stack variations.
According to still another aspect of the present invention, there is provided a method for aligning a semiconductor wafer and a mask. A semiconductor wafer is provided having a film stack from which light is reflected and an alignment mark formed on the semiconductor wafer. A mask is provided having a pattern formed thereon. The mask is illuminated so as to create a bright spot thereon by a 0_xcfx80 phase conflict during an illumination. The bright spot is independent of variations of the film stack. The alignment mark is aligned with respect to the bright spot, so as to align the semiconductor wafer with the mask independent of the variations of the film stack.
According to still yet another aspect of the present invention, there is provided a system for aligning a semiconductor wafer and a mask. An illumination tool irradiates the mask so as create a bright spot thereon by a 0_xcfx80 phase conflict during an illumination. A detection tool detects the bright spot and the alignment mark. Alignment means aligns the alignment mark with the bright spot so as to align the semiconductor wafer with the mask.
These and other aspects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings.